1. The Field of the Invention
The present invention relates to optical devices usable within an optical network. More particularly, the present invention relates to using full-ball lenses in an add/drop module of an optical device.
2. Background of the Invention
Optical add/drop modules are commonly used in existing optical communications networks. These add/drop modules may include add/drop multiplexers (OADM), add/drop de-multiplexers (OADDM), and other types of add/drop optical components. A multiplexer enables multiple carrier waves to be carried on a single transmission medium by combining the multiple carrier waves into a single carrier wave that propagates along the optical fiber.
The multiple carrier waves are at different frequencies and separated by some predetermined amount of frequency separation. This frequency separation is known as the channel spacing. Combining the multiple signals into a single carrier signal reduces the number of fiber cables that must be laid in order to transmit a required amount of data. Depending on the type of cable and the number of individual channels combined into the cable, a significant increase in overall data transmission rates may be achieved using OADMs.
At a location remote from the OADM is an optical add/drop de-multiplexer (OADDM) that separates the different wavelengths from the multiplexed carrier signals and transmits each of these wavelengths to their own individual receivers. Alternately, the OADDM might drop one or more single channels from the propagating signal. The data on these channels is received by a receiver specifically tuned to the frequency of that channel and which performs the optical to electrical conversions accordingly. The remaining channels are forwarded to the next node without being routed through a receiver. The use of OADMs and OADDMs in optical networks has increased significantly over the last few years, particularly as the channel spacing has been reduced from about 200 GHz for Dense Wavelength Division Multiplexing (DWDM) systems to about 25 GHz for Ultra-Dense Wavelength Division Multiplexing (UDWDM) systems.
Typically, one or more graded or gradient index (GRIN) lenses are used in optical communications equipment and imaging systems, such as optical add/drop multiplexers and de-multiplexers. Rods or optical fibers, and even a relatively flat piece of optical material, may function as a GRIN lens. Unfortunately, relatively precise and sometimes tedious alignment procedures are often required during fabrication and assembly of optical communications equipment using GRIN lenses. Also, the cost of optical communications equipment having one or more GRIN lenses may be high due to the requirement for the use of high precision mechanical parts to maintain desired optical alignment.
In addition to the cost aspects of using GRIN lenses, issues arise from the large beam diameter associated with the GRIN lens. Specifically, currently available GRIN lenses that have a relatively large beam diameter may conflict with aperture requirements and stability requirements of associated optical mechanical components.
In an attempt to alleviate the problems associated with GRIN lenses, optical add/drop modules have previously been manufactured using two half-ball lenses with a beam splitting filter disposed between the half-ball lenses. Unfortunately, this approach is as problematic as using a GRIN lens. For instance, cutting a full-ball lens and polishing the resulting half ball lenses can be expensive. Additionally, aligning the half ball lenses within an optical component can be both expensive and time consuming due to the precise alignment procedures required for packaging discrete optical components.